Method and system for secure access to a vehicle

ABSTRACT

A method for assessing a reliability of a determination of the relative position between a device for accessing a vehicle and the vehicle including transmitting a first radio signal from a first antenna of the vehicle; transmitting a second radio signal from a second antenna of the vehicle; receiving the first radio signal at the device and determining a first signal intensity; receiving the second radio signal at the device and determining a second signal intensity; determining, at the device or the vehicle, a relative position of the device and/or the vehicle and/or signal directions from which the radio signals have arrived at the device, based on the first signal intensity and the second signal intensity; determining a compatibility of the determined relative position and/or the signal directions with an arrangement of the first antenna and the second antenna at the vehicle to assess the reliability of relative position determination.

PRIORITY CLAIM

This patent application claims priority to German Patent Application No.10 2016 207 997.2, filed 10 May 2016, the disclosure of which isincorporated herein by reference in its entirety.

SUMMARY

Illustrative embodiments relate to a method for assessing a reliabilityof a determination of the relative position between a device foraccessing a vehicle and the vehicle, a method for allowing or denyingaccess to a vehicle, and a system for allowing or denying access to avehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

Disclosed embodiments will now be explained with reference to theattached drawings.

FIG. 1 illustrates a schematic view of a relay attack using a keylessentry system according to the related art;

FIG. 2 illustrates a schematic representation of a system for allowingor denying access to a vehicle according to a disclosed embodiment; and

FIG. 3 illustrates a flow chart of a method for assessing a reliabilityof a determination of the relative position between a device foraccessing a vehicle and the vehicle according to a disclosed embodiment.

DETAILED DESCRIPTION

DE 41 23 654 A1 discloses a method for detecting a portable transponderenclosed in the vehicle interior for keyless access to the vehicle,wherein the position of the transponder is detected and a signal istriggered, wherein locking is carried out only if the transponder isdetected outside the vehicle. Information about the position of thetransponder is obtained from the field strength distribution of thetransponder. In addition to determining the position of the transponder,a movement tendency of the transponder may also be detected from thefield strength changes and from the field strength change distributionof code signals which are transmitted in succession by the transponder.

DE 199 00 415 B4 discloses a method for carrying out a keyless securityentry control method for motor vehicles, wherein a transceiver deviceand an identification transmitter are provided in the motor vehicle. Theinstantaneous position of the identification transmitter is determined,namely, via the identification transmitter itself. Furthermore, aplausibility check with respect to the action signal received by theidentification transmitter is carried out as a function of itspreviously determined position. To open the vehicle, the person carryingthe ID transmitter actuates the door handle on the driver's door,whereupon the request to unlock the door is conveyed via a toggle switchto the transceiver device, whereupon the transceiver device respondswith the start of a query-response dialog. Wake-up signals aretransmitted via LF transmitters for activating ID transmitters situatedin the reception range of these LF transmitters. Subsequently,location-coded LF signals are transmitted via the LF transmitters.Furthermore, a determination of the position of the ID transmitterssituated in the reception range of the LF transmitters is carried out.

Keyless entry systems in vehicles may be susceptible to so-called relayattacks, in which the distance between the vehicle and the radio key isbridged by two transceiver units in such a way that opening and startingthe vehicle is possible even if the key is actually outside the range,as described in the magazine c't, no. 26/2015. To detect or impede relayattacks, various approaches are followed in the related art. Initially,measures for securing the frequency bands (generally LF and UHF) usedfor the radio communication, for example, RSSI measurements andamplitude hopping, were carried out. Furthermore, measurements viaadditional use of other frequency bands, for example, UWB withtime-of-flight (ToF) measurement and phase difference measurement, werecarried out. Furthermore, measurements independent of radio technology,for example, checking the geographical proximity between the key and thevehicle via GPS (Global Positioning System), were carried out.

However, the conventionally known methods and measures are for the mostpart very elaborate, complex and costly. The effectiveness of some ofthe known methods may also be reduced or even rendered completelyinoperable by unauthorized persons such as thieves. Furthermore, knownmethods may be subject to location-dependent limitations (for example,GPS inside parking garages).

Disclosed embodiments describe and provide a method for assessing areliability of a determination of the relative position between a devicefor accessing a vehicle and the vehicle, a method for allowing ordenying access to a vehicle, and a system for allowing or denying accessto a vehicle, wherein at least some of the drawbacks arising in therelated art are overcome. Disclosed embodiments provide a method and asystem which impede or even completely prevent access to a vehicle byunauthorized persons.

According to at least one disclosed embodiment, a method for assessing areliability of a determination of the relative position between a devicefor accessing a vehicle and the vehicle. The method refers totransmission of a first radio signal from a first antenna of thevehicle; transmission of a second radio signal from a second antenna ofthe vehicle; reception of the first radio signal at the device anddetermination of a first signal intensity; reception of the second radiosignal at the device and determination of a second signal intensity;determination, at the device or the vehicle, of a relative position ofthe device and the vehicle and of signal directions from which the radiosignals have arrived at the device, based on the first signal intensityand the second signal intensity; determination of a compatibility of thedetermined relative position and the signal directions with anarrangement of the first antenna and the second antenna on the vehicle,to assess the reliability of the relative position determination.

The method may, for example, be carried out by a device inside thevehicle and by a mobile device, for instance, a mobile electronic key.Disclosed embodiments may improve keyless access to a vehicle. Forexample, if a hand of an authorized driver comes within a certaindistance of a door handle of a vehicle equipped with a keyless entrysystem, the corresponding system is activated from a sleep mode.Furthermore, an encoded query signal at a LF frequency of, for example,125 or 130 kHz may be transmitted via one or multiple antennasdistributed on or in the vehicle. Thereupon, the system may switch to areception mode in the UHF range (for example, 433 MHz or 868 MHz forEurope, or 315 MHz for Japan and the USA), and wait for a confirmation.If the device, i.e., the electronic key which may be configured as anRFID transponder, is in a range (of several meters), it receives the LFquery signal, may decode it, and may retransmit it in the UHF frequencyband having new encoding. This signal transmitted by the electronic keymay be decoded again in the vehicle. In this case, the system inside thevehicle may know both the encoding table of the electronic key and itsown encoding table, and may thus compare its own original transmissionto the signal just received. If there is no correct response within adefined period, the system may switch again to a waiting mode. If thetwo codes match, the system may effectuate an authorization, whereby thesystem may release the lock of the vehicle. The door can thus be openedby pulling on the handle.

To impede or even prevent a possible relay attack by unauthorizedpersons, a first radio signal and a second radio signal are transmittedrespectively by the first antenna and the second antenna (arranged inanother area) of the vehicle. The two signals are received by thedevice, and a respective signal intensity is determined. The first radiosignal may have been transmitted at a known, original first signalintensity, and the second radio signal may have been transmitted at aknown, original second signal intensity. In the case of a known,original first signal intensity and a known, original second signalintensity, a determination of the first signal intensity and the secondsignal intensity of the radio signals received at the device providesinferences about the distance between the first antenna of the vehicleand the device, and inferences about the distance between the secondantenna of the vehicle and the device. Furthermore, additional radiosignals may optionally be transmitted by the vehicle from otherantennas, and received by the device, and their signal intensities mayalso be determined. A position of the device relative to the vehicle(described, for example, in a coordinate system which is fixedly relatedto the vehicle) may thereby be determined.

The device may furthermore comprise an antenna or an antenna systemhaving multiple antenna sections, the antenna system being able to allowthe determination of a direction from which a specific radio signal hasbeen received. For example, for this purpose, a so-called 3D antenna maybe used, which may comprise two or three or even more antenna sectionswhich are oriented in different directions which, for example, areperpendicular to one another. Signal intensities which are determined bythe various antenna sections may provide information about the directionfrom which the relevant radio signal was received.

The device and/or the vehicle may also have information about thearrangement of the first antenna and the second antenna (and otherantennas) on the vehicle. After the relative position and the signaldirections from which the radio signals have arrived at the device havebeen determined, a plausibility check of the relative position and thesignal directions may be carried out by checking whether the determinedrelative position and the signal directions are consistent, i.e.,compatible, with the known arrangement of the antennas. Thecompatibility may be characterized by a quantitative variable. Thecompatibility may, for example, be characterized by specific categories,for example, high compatibility, average compatibility, or lowcompatibility. The reliability may also be characterized by a number orclass or category which represents the degree of reliability. Thus, aplausibility check of the relative position of the device relative tothe vehicle may be carried out, and may be used to ensure controlledaccess to the vehicle.

The device may comprise an antenna having at least two antenna sectionsoriented along two directions, the antenna being configured to determinethe signal strength components of received signals associated with thetwo directions. The device may comprise an antenna with three antennasections oriented along three directions, to be configured to be able todetermine the direction of a radio signal when one is received. Thus,the method may be implemented via conventionally available antennas, forexample, a 3D antenna.

The method may furthermore comprise transmission of a third radio signalfrom a third antenna of the vehicle, and reception of the third radiosignal at the device and determination of a third signal intensity.Additional radio signals which are transmitted from additional antennasof the vehicle, or additional radio signals which are repeatedlytransmitted by identical antennas, may be received at the device. Theaccuracy of a relative position determination may be increased byreceiving and evaluating more radio signals from more antennas. A signalintensity of a radio signal may decrease with a specific characteristiccurve, as a function of the distance from the transmitting antenna, forexample, quadratically with the distance. It is possible to infer thedistance between the transmitting antenna and the position of the devicefrom a ratio of the original signal intensity (at the transmittingantenna) and the signal intensity which was received at the device. Inthe case of three transmitting antennas which transmit three (differentor identical) radio signals, the position of the device relative to thevehicle may be obtained via the intersection of three spheres, eachhaving the relevant transmitting antenna in the center, and having aradius which is determined as a function of the received signalintensity and/or the original signal intensity. Furthermore, theorientation of the device (for example, relative to the vehicle) may bedefined by determining the directions of the radio signals. However, adetermined relative position and determined directions or orientationmay not always, for example, in the case of a relay attack, consistentwith the known arrangement of the antennas from which the radio signalshave been transmitted. If an inconsistency is determined, thecompatibility of the determined relative position and the signaldirections with the known antenna arrangement is classified as low, or acorrespondingly low numerical value is assigned. Thus, the reliabilityof the relative position determination is also assessed as low. However,if a consistency between the position, the signal directions, and theantenna arrangement is ascertained, a high compatibility may bedetermined, and the reliability of the relative position determinationmay thus be assessed as high.

The method may furthermore comprise a measurement of the terrestrialmagnetic field direction at the vehicle, for example, via a sensorinside the vehicle. Furthermore, a terrestrial magnetic field directionmay also be measured at the device (using a sensor which is incorporatedinto the device). Furthermore, the terrestrial magnetic field directionat the vehicle (the one which was measured at the vehicle) may becompared with the one at the device, for instance, the one which wasmeasured at the device, to further assess the reliability of therelative position determination. At a specific relative position andorientation (from the specific signal directions) of the device relativeto the vehicle which are correct, a particular terrestrial magneticfield direction is expected at the device which is consistent with, inparticular is parallel to, the terrestrial magnetic field direction atthe vehicle. However, if the device determines a terrestrial magneticfield direction which, for example, is not (or is not essentially)parallel to the terrestrial magnetic field direction determined by thevehicle, this may be an indication that either the determination of therelative position and/or an orientation of the device is not reliable orhas only a certain degree of reliability. An assessment of thereliability of the relative position determination may thereby befurther improved.

The method may furthermore comprise determination of a compatibility ofthe particular terrestrial magnetic field directions at the vehicle andat the device via the arrangement at least of the first antenna and thesecond antenna at the vehicle, to further determine the reliability ofthe determination of the relative position and/or a particular relativeorientation between the device and the vehicle. The method may therebybe further improved.

The method may furthermore comprise a generation of an additionalmagnetic field at the vehicle (for instance, by activating coils of anelectric motor, such as supplying the coil with direct current), toobtain a total magnetic field which is not only detectable inside thevehicle, but also radiates or is perceptible or detectable in animmediate vicinity of the vehicle. The total magnetic field can bemeasured at the device, i.e., the magnetic field direction (andoptionally also the intensity) of the total magnetic field can bemeasured at the location of the device. Furthermore, the measured totalmagnetic field at the device may be compared to an expected totalmagnetic field at the device according to the generated additionalmagnetic field, the determined relative position and/or relativeorientation, to continue to assess the reliability of the determinationof the relative position and/or a determined relative orientationbetween the device and the vehicle.

A brief magnetic field disturbance of the otherwise constant terrestrialmagnetic field may be caused by activating a magnetic field-generatingdevice inside the vehicle. The total magnetic field and/or the change inthe magnetic field may be detected at the device with respect to itsdirection and/or strength, and may furthermore be used for assessing thereliability of the relative position determination.

The method may furthermore comprise a wireless transmission ofmeasurement data, which relate to the signal intensities and/or signaldirections and/or magnetic fields, from the device to the vehicle. Anevaluation of these measurement data with respect to the relativeposition determination and/or orientation determination and/or signaldirection determination and/or assessment of the reliability of therelative position determination may be carried out at the vehicle (in acorresponding control unit or in a processing unit). As a result, thecomplexity of the device and the energy consumption of the device may bereduced. The device does not have to allow any extraordinary processingprocesses and may thus be configured and provided in a simple,economical manner.

It should be understood that features which have been mentioned,provided, described, or explained individually or in any combination inconnection with a method for assessing a reliability of a determinationof the relative position, may also be used individually or in anycombination on a method for allowing or denying access to a vehicle, andalso on a system for allowing or denying access to a vehicle, accordingto disclosed embodiments.

According to another disclosed embodiment, a method is provided forallowing or denying access to a vehicle. In this case, the methodcomprises arranging a device for accessing the vehicle with respect tothe vehicle; carrying out a method for assessing a reliability of adetermination of the relative position between the device and thevehicle according to one of the preceding disclosed embodiments;depending on the degree of reliability: allowing or denying access tothe vehicle, wherein allowing the access comprises opening a lock of avehicle door and/or starting an engine of the vehicle.

Thus, access to a vehicle may be made possible only for authorizedpersons; the effects of relay attacks may be limited.

According to at least one disclosed embodiment, a system for allowing ordenying access to a vehicle is provided. The system comprises thevehicle and a device for accessing the vehicle, wherein the system isconfigured to carry out the method for allowing or denying access to thevehicle according to an above-described embodiment.

FIG. 1 illustrates a vehicle 70 which may be opened using an electronickey 72 of an authorized person 74 (adapted from c't, no. 26/2015). Thekey 72 is an electronic key which can grant access to the vehicle 70according to a conventional keyless entry system, wherein the key, forexample, can trigger a lock of a door of the vehicle 70 to open. Insidethe conventional keyless entry system, an arrangement of the key 72 nearthe vehicle, for example, within a distance of 1 m, is required to opena door of the vehicle 70. To gain unauthorized access to the vehicle 70,an unauthorized person 76, for example, a thief, positions him/herselfin an immediate vicinity of the vehicle 70, a transceiver device 82intercepts radio signals from the vehicle 70, and relays them to anotherunauthorized person 78 who is situated near the authorized person 74.Signals transmitted by the key 72 are also transmitted from atransceiver unit 80 of the other unauthorized person 78 to acorresponding transceiver device 82 of the first unauthorized person 76,who transmits this radio signal onwards to the vehicle 70.

Thus, the car thieves 76 and 78 have radio relays 82 and 80 whichmutually relay the signals from the vehicle 70 and the key 72. The thiefis therefore able to open and start the car after the owner 74 havingthe key 72 has departed.

FIG. 2 schematically illustrates a system 1 for allowing or denyingaccess to a vehicle 3 according to at least one disclosed embodiment.The system 1 comprises the vehicle 3 and a device 5 which, for example,may comprise an electronic key for gaining access (for example, openinga door and/or starting an engine and/or operating the vehicle fordriving) to the vehicle 3, for example, by opening a side door of thevehicle 3.

The system 1 is configured to carry out a method for allowing anddenying access to a vehicle according to at least one disclosedembodiment. This method also comprises carrying out a method 7 forassessing a reliability of a determination of the relative positionbetween the device 5 and the vehicle 3 according to at least onedisclosed embodiment, the method 7 being depicted in FIG. 3 as a flowchart. In a method operation at 9, a first radio signal 13 (for example,a LF or HF or UHF signal) is transmitted from a first antenna 11 of thevehicle 3, having a known original first signal intensity. In methodoperation at 15, a second radio signal 19 (for example, a LF or HF orUHF signal) is transmitted from a second antenna 17 of the vehicle 3,having a known second original signal intensity. In a method operationat 21, the device 5 receives the first radio signal 13 and determines afirst signal intensity. In an additional method operation at 23, thedevice 5 receives the second radio signal 19 and determines a secondsignal intensity, i.e., the intensity of the second radio signal 19received at the device 5. In a method operation at 25, a relativeposition (xG, yG, zG) (for example, with respect to a vehicle coordinatesystem having coordinate axes x, y, z) of the device 5 and the vehicle3, as well as signal directions (i.e., the directions from which theradio signals 13 and 19 have been received at the device 5), isdetermined at the device 5 or the vehicle 3, based at least on the firstsignal intensity and the second signal intensity. In a further methodoperation at 27, a compatibility of the determined relative position(xG, yG, zG) and the signal directions 13, 19 with an arrangement of theantennas 11 and 17 on the vehicle is determined at the device 5 or atthe vehicle 3, to assess the reliability of the relative positiondetermination. It may be detected whether all received radio signalscome from the same direction. In such a case, there is a highprobability that a relay attack may be taking place (as a function ofthe antenna positions, if not all antennas are in the same direction inthe calculated position).

In this case, the method 7 may be carried out within a method forallowing or denying access to a vehicle 3, wherein here, afterdetermining the degree of reliability, access to the vehicle 3 isallowed or denied. If, for example, a high degree of reliability of thedetermined relative position (xG, yG, zG) has been determined, a door ofthe vehicle 3 may be opened according to, or with the aid of, additionalsignal exchanges between the vehicle 3 and the device, 5 according toone conventional keyless entry method.

If, for example, a high reliability of the determined relative positionhas been determined, and the device 5 is situated within a predeterminedradius around the vehicle 3, the vehicle may transmit an encoded querysignal 29, for example, at an LF frequency. Thereupon, the vehicle 3 ora transceiver system 4 comprised therein, which is connected to thefirst antenna 11, the second antenna 17, and also to a third antenna 12,may switch to a receive mode, for example, in the UHF range (forexample, 433 MHz in Europe, or 868 MHz or 315 MHz in Japan or in theUSA) and wait for a confirmation from the device 5. If the device 5(which may be configured as an RFID transponder) is situated within anarea 31 which constitutes an acceptable vicinity of the vehicle 3, thedevice 5 receives the encoded signal 29 from the vehicle 3. The device 5may then decode the signal 29 and retransmit it, having new encoding, asa signal 33 (for example, in the UHF frequency range). The vehicle 3receives the signal 33 transmitted by the device 5 via one (or aplurality) of the antennas 11, 12, 17 and decodes it. Since thekeyless-go control unit 6 which is included in the vehicle 3 knows bothencoding tables, it may compare its own original transmission with thesignal 33 just received. If there is no response within a definedperiod, the system 1 may again switch to a standby mode. If thetransmitted signal 33 decoded by the device 5 matches the signal 29transmitted by the vehicle 3, access to the vehicle 3 may be granted.

Since, according to at least one disclosed embodiment, a degree ofreliability of the relative position determination of the device 5 isconsidered when allowing or denying access to the vehicle 3, the risk ofa relay attack as depicted in FIG. 1 may be reduced.

The vehicle 3 may be equipped with a magnetic field sensor 35, whichallows determining the terrestrial magnetic field, such as the directionof the terrestrial magnetic field 37. The device 5, which is equippedwith a transceiver system 2, may also comprise a magnetic fielddetection system 39, also to be able to determine a terrestrial magneticfield direction 41 at the device 5. The method carried out by the system1 may furthermore comprise a comparison of the terrestrial magneticfield direction 37 at the vehicle 3 and the terrestrial magnetic fielddirection 41 at the device, to further assess the reliability of therelative position determination.

Information ascertained at the device about signal intensities of thesignals 19, 33, and about signal directions, and/or about theterrestrial magnetic field, etc., may be transmitted to the vehicle viasignals 30.

The vehicle 3 may furthermore comprise an electric machine 43, forinstance, an electric motor, for example, a drive motor or an alternatoror the like, which is able to generate an additional magnetic field 45at the vehicle 3 to obtain a total magnetic field 47. The total magneticfield 47 may be obtained as a superimposition of the terrestrialmagnetic field 37 and the additional magnetic field 45, and may also bemeasured by the sensor 35. The total magnetic field 49 and/or its change50 may furthermore be measured at the device 5. The total magnetic field49 measured at the device may then be compared to an expected totalmagnetic field 51 which is derived from the additionally generatedmagnetic field 45, the determined relative position, and/or a relativeorientation, to continue to assess the reliability of the determinationof the relative position and/or a determined relative orientationbetween the device and the vehicle.

For receiving the first signal 13 and the second radio signal 19 andoptionally additional radio signals from the vehicle 3, the devicecomprises an antenna 8 which, for example, may be configured as a 3Dantenna, to be able to determine the direction from which the determinedradio signals arrive. An orientation 53 of the device 5, which, forexample, may represent the direction of a longitudinal axis of thedevice, may be determined from the determined directions.

The processing of the data for the determination of the relativeposition and/or an orientation of the device may be carried out in thevehicle 3, for instance, in the control unit 6, for which purposecorresponding data about signal(s) 30 may be transmitted from the device5 to the vehicle 3.

Disclosed embodiments enable an evaluation and plausibility check of thelocal terrestrial magnetic field in relation to the direction ofreception of the radio signals between the key and the vehicle. Forexample, the following method operations may be carried out:

-   1. The vehicle 3 transmits a query 13, 19 to the radio key 5. Here,    multiple antennas 11, 12 and/or 17 are used at least for a portion    of the radio combination.-   2. The radio key 5 receives the query 13, 19 from the vehicle and,    upon receiving the signals of the various antennas, ascertains data    which, in the case of a known antenna configuration, allow making an    inference about the position of the key 5 (for example, field    strength measurement, etc.).-   3. Both the vehicle 3 and the key measure the local terrestrial    magnetic field (37, 41) and relate it to the antennas 11, 12, 17    installed in the vehicle, and to the ascertained position and    orientation of the key 5.-   4. The position and orientation of the key 5 are    plausibility-checked against the measured magnetic field.

It may thus be checked whether the key 5 is actually situated in thevicinity of the vehicle 3 or whether the position is consistentlydetermined, also considering the measurement of the receptiondirections.

Thus, it may be assumed that the local terrestrial magnetic fieldgenerally changes only slightly in the immediate vicinity of thevehicle. Possible sources of interference (for example, steel beams inbuildings) may affect the magnetic field, but act equally on the vehicleand the key, so that the magnetic field may still be used for thismeasure.

According to at least one disclosed embodiment, the device 5 mayascertain the local magnetic field 41 in all three spatial axes, andtransmit it to the vehicle 3 along with the ascertained receptionstrengths and directions of the radio signals 13 and 19. The vehicle 3may thus be enabled to check whether the magnetic field of the keymatches its own magnetic field 37 (and/or 47), considering the positionof the key ascertained from the reception strengths and directions. Inthis case, the transmission of data between the device and the vehicle 3using conventional measures may be secured, for example, via encryption,signing, etc.

According to an enhancement of the method, during the communication, thevehicle may selectively influence the local terrestrial magnetic field,and it may subsequently be validated whether the key actually detectsthe influence, as expected. If the key 5 detects the influence, it maybe determined whether the change is plausible in relation to themeasured distance and direction. In this case, the influence of themagnetic field may take place by briefly switching on electrical devicesin the vehicle, for example, the radio, loudspeakers, etc. orelectromagnets specifically installed for this purpose. In addition, inthe case of electric vehicles, the magnetic field may also be influencedby selectively supplying current to the electric motor (for instance,via direct current, i.e., static current), the brakes, and/or the coilfor inductive charging.

In addition, the device 5 may carry out a measurement of the gravitationto ascertain its orientation in space, and also to be able to factor inthe gravitation when validating the magnetic field.

Furthermore, in addition to the direction of the magnetic field withrespect to the position of the key, it is also conceivable to perform aplausibility check of the direction of motion of the key. For example,if the key is moving away from the vehicle, unlocking is notpermissible.

The evaluation and plausibility check of the magnetic field within thescope of the measure may also take place in the key (instead of thevehicle), independently of the above-described enhancements.

The measure may also be applied to other devices used for access,independently of the disclosed embodiment, for example, smartphones andsmartwatches, to protect them from relay attacks. This may possibly evenbe carried out in the devices without additional hardware expense, sincein any case, they could have already been equipped with sensors fordetecting the magnetic field (and gravitation).

The evaluation of the measured data may possibly be complex and may forthis purpose take place in the vehicle or in a processor of the vehicle.If the processing is carried out in the vehicle 3, calculating power maybe saved at the device 5, and the hardware may be designed in a simplemanner. Furthermore, energy consumption may be reduced. The plausibilitycheck of the measured magnetic field may take place inside the vehicle3. The key 5 may transmit the detected measurement data to the vehiclefor this purpose. If a plausibility check takes place in the key, and ifthe key transmits only an “acknowledge” to the vehicle, the transmissionis possibly significantly easier to bypass, even when using suitablesecurity measures, and the signal could correspondingly be changedwithin the scope of a relay attack in such a way that a positiveresponse arrives at the vehicle even if the magnetic fields do notmatch.

The plausibility check of the measure magnetic field may furthermorerequire specific information about the positions of the antennas 11, 12and 17 in the vehicle 3, the field characteristic due to the influenceof the vehicle shell, and about the antenna parameters used (forexample, current supply). If a plausibility check were to take place inthe key, these data would have to be correspondingly stored in thealgorithm in the key. This may lead to side effects:

The cumulation must possibly include more data (transmission of theinformation for each plausibility check).

The training of a key must possibly be expanded to include thecorresponding data (one-time transmission of the information andsubsequent storage in the key).

Alternatively, the key must obtain the required information duringproduction. As a result, subsequent changes (for example, softwareupdates of the vehicle) may no longer be possible under somecircumstances, or it may no longer be possible for a structurallyidentical key to be provided under some circumstances for multiplevehicle types, since the parameters differ too much.

The detection of a selected peak in the magnetic field according to atleast one disclosed embodiment, caused by a corresponding device in thevehicle, allows only inferences to be made about a geographicalproximity and possibly about an approximate distance (evaluation of thesignal strength of the measured peak), but not plausibility checkingwith respect to a position. Therefore, this disclosed embodiment may beviewed as support for other embodiments.

The generation of an additional magnetic field described in thisembodiment could, however, also be applied as a sole measure. In thiscase, a plausibility check of the local terrestrial magnetic field withrespect to the key position would be omitted; instead, only thesimultaneous presence of a transient change in the magnetic field wouldbe interpreted as an indication of the geographical proximity of the keyand vehicle. Although this would considerably simplify the detection andprocessing, the security of the measure would also decrease, since amagnetic pulse could also be “relayed” using corresponding technology.“Relaying” a magnetic field is possibly only with great effort;therefore, disclosed embodiments may enable access only to persons whoare actually authorized.

Disclosed embodiments may be transmitted to conventional radio keys, toprotect them from manipulation in which the signal of the radio remotecontrol is recorded and later transmitted.

LIST OF REFERENCE NUMERALS

-   1 System-   3 Vehicle-   2 Transceiver device-   4 Transceiver device-   5 Device-   6 Keyless entry control system-   7 Method-   9, 15, 21, 23, 25, 27 Method operations-   8 Antenna of the device-   11, 12, 17 Antennas of the vehicle-   13 First signal-   19 Second signal-   29 Encoded signal-   30 Signal from device-   31 Radius around vehicle-   33 Signal encoded by the device-   35, 39 Magnetic field detection devices-   37 Terrestrial magnetic field at vehicle-   41 Terrestrial magnetic field at device-   43 Electric machine-   45 Additional magnetic field-   47 Total magnetic field at the vehicle-   49 Total magnetic field at the device-   51 Expected total magnetic field at device-   53 Orientation of the device-   xG, yG, Zg Relative position of the device

1. A method for assessing a reliability of a determination of therelative position between a device for accessing a vehicle and thevehicle, the method comprising: transmitting a first radio signal from afirst antenna of the vehicle; transmitting a second radio signal from asecond antenna of the vehicle; receiving the first radio signal at thedevice and determining a first signal intensity; receiving the secondradio signal at the device and determining a second signal intensity;determining, at the device or the vehicle, a relative position of thedevice and the vehicle and/or signal directions from which the radiosignals have arrived at the device, based on the first signal intensityand the second signal intensity; determining a compatibility of thedetermined relative position and/or the signal directions with anarrangement of the first antenna and the second antenna at the vehicle,to assess the reliability of the relative position determination;measuring a magnetic field direction at the vehicle; measuring amagnetic field direction at the device; and comparing the magnetic fielddirection at the vehicle and at the device to further assess thereliability of the relative position determination.
 2. The method ofclaim 1, wherein the device comprises an antenna having at least twoantenna sections oriented along two directions, the antenna determinesthe signal strength components of received signals associated with twodirections.
 3. The method of claim 1, further comprising: transmitting athird radio signal from a third antenna of the vehicle; and receivingthe third radio signal at the device and determining a third signalintensity, wherein the determination of the relative position of thedevice and the vehicle and the signal directions is based on the thirdsignal intensity.
 4. The method of claim 1, further comprising:determining a compatibility of the determined terrestrial magnetic fielddirection at the vehicle and at the device with the arrangement at leastof the first antenna and the second antenna at the vehicle to furtherdetermine the reliability of the determination of the relative positionand/or a determined relative orientation between the device and thevehicle.
 5. The method of claim 1, further comprising: generating anadditional magnetic field at the vehicle to obtain a total magneticfield; measuring the total magnetic field at the device; comparing themeasured total magnetic field at the device to an expected totalmagnetic field at the device according to the generated additionalmagnetic field, the determined relative position and/or relativeorientation to continue to assess the reliability of the determinationof the relative position and/or a determined relative orientationbetween the device and the vehicle.
 6. The method of claim 1, furthercomprising wirelessly transmitting measurement data, which relate to thesignal intensities and/or signal directions and/or magnetic fields, fromthe device to the vehicle.
 7. The method of claim 1, wherein the deviceis a user-wearable device and/or comprises an electronic key of thevehicle.
 8. A method for permitting or denying access to a vehicle, themethod comprising: arranging a device for accessing the vehicle withrespect to the vehicle; assessing a reliability of a determination ofthe relative position between the device and the vehicle, wherein theassessment comprises: transmitting a first radio signal from a firstantenna of the vehicle; transmitting a second radio signal from a secondantenna of the vehicle; receiving the first radio signal at the deviceand determining a first signal intensity; receiving the second radiosignal at the device and determining a second signal intensity;determining, at the device or the vehicle, a relative position of thedevice and the vehicle and/or signal directions from which the radiosignals have arrived at the device, based on the first signal intensityand the second signal intensity; determining a compatibility of thedetermined relative position and/or the signal directions with anarrangement of the first antenna and the second antenna at the vehicle,to assess the reliability of the relative position determination;measuring a magnetic field direction at the vehicle; measuring amagnetic field direction at the device; and comparing the magnetic fielddirection at the vehicle and at the device to further assess thereliability of the relative position determination; and permitting ordenying access to the vehicle on the degree of reliability, whereinpermitting the access comprises opening a lock of a vehicle door and/orstarting an engine of the vehicle.
 9. A system for permitting or denyingaccess to a vehicle, the system comprising: a vehicle; and a device foraccessing the vehicle, wherein a reliability of a determination of therelative position is performed between the device for accessing avehicle and the vehicle, wherein the reliability determinationcomprises: transmitting a first radio signal from a first antenna of thevehicle; transmitting a second radio signal from a second antenna of thevehicle; receiving the first radio signal at the device and determininga first signal intensity; receiving the second radio signal at thedevice and determining a second signal intensity; determining, at thedevice or the vehicle, a relative position of the device and the vehicleand/or signal directions from which the radio signals have arrived atthe device, based on the first signal intensity and the second signalintensity; determining a compatibility of the determined relativeposition and/or the signal directions with an arrangement of the firstantenna and the second antenna at the vehicle, to assess the reliabilityof the relative position determination; measuring a magnetic fielddirection at the vehicle; measuring a magnetic field direction at thedevice; and comparing the magnetic field direction at the vehicle and atthe device to further assess the reliability of the relative positiondetermination.